The present invention relates to fiber optic telecommunications access networks and, in particular, to a novel optical network unit and host digital terminal for use in such networks.
The development of telecommunications access network architectures for delivering narrowband and broadband services from a central office straight into subscribers"" homes has been prompted by the public""s growing demand both for broadband applications, such as Web browsing and teleconferencing, and for more traditional narrowband services, such as telephony.
In certain kinds of access networks, known as xe2x80x9cfiber-to-the-neighbourhoodxe2x80x9d (FTTN) or xe2x80x9cfiber-to-the-curbxe2x80x9d (FTTC) networks, a host digital terminal (HDT) is typically used for delivering the various communications services to customer premises equipment (CPE) via a communications path that is part optical fiber and part copper twisted pair. Optical network units (ONUs) are used for interfacing between optical fibers connected to the HDT and sets of twisted pairs connected to the CPE at each subscriber""s home.
Currently, different types of ONUs are used depending on whether the communications service to be delivered is of the narrowband or broadband variety. For example, a specialized narrowband ONU may perform the conversion of mu-law compressed voice samples arriving from the HDT into linear samples for delivery to a customer""s telephone. In another scenario, the narrowband ONU may be required to convert DS-1 digital data arriving from an analog modem at the customer premises into a cell-based data structure to be delivered to the HDT.
From these and many other conceivable examples, it is apparent that a narrowband ONU must perform various complex processing tasks. Traditionally, this is achieved with the aid of mission-specific or service-specific line cards, although the number of line card types can be reduced by the deployment of powerful digital signal processing (DSP) engines on some or all of the line cards to allow them to adapt their functions, thereby to provide a wider range of service types. Still, conventional narrowband ONUs have severe drawbacks, such as high cost, high power consumption, low reliability and overall large physical volume.
Some of the disadvantages of a conventional narrowband ONU can be mitigated by simplifying its design. This has been recognized in above-mentioned U.S patent application Ser. No. 09/056,096, which discloses a line card structure that considerably streamlines a narrowband ONU by relegating the majority of the complex, service-specific and power-hungry signal processing operations to the HDT.
A completely different type of ONU is required when contemplating the delivery of broadband services (based on, e.g., asynchronous transfer mode-ATM or Internet protocol-IP), which are typically asynchronous and packet-based. In this case, problems arise when the peak data rate demanded by a particular subscriber exceeds the data rate available on an individual copper drop leading to that subscriber""s CPE. Similarly, it is not uncommon for the aggregate data rate transmitted by multiple subscribers to exceed the bandwidth available on the fiber leading to the HDT. In both situations, data is caused to accumulate in the ONU, usually leading to an unacceptable delay and/or loss of data.
One technique used to help prevent bottlenecks from appearing at a broadband ONU consists of installing memory buffers (xe2x80x9cqueuesxe2x80x9d) in the ONU for storing excess data until it can be delivered. The buffer size required to safeguard against data loss is a function of the peak bandwidth demand as well as the duration of such a demand. However, neither of these two parameters is controllable, leading to the installation of very long queues in the ONU for handling an estimated worst-case scenario. Furthermore, it is necessary to implement a complex and power-intensive queueing structure in order to avoid the situation in which higher priority traffic elements (e.g., cells) are xe2x80x9ctrappedxe2x80x9d among lower priority traffic elements within the queue.
As with narrowband ONUs, some of the disadvantages of conventional broadband ONUs can also be mitigated by simplifying the ONU design. For instance, above-mentioned U.S. patent application Ser. No. 09/084,370 discloses a method of controlling traffic flow at the HDT which allows the use of queues in the ONU that are significantly reduced in size and complexity, again diminishing the ONU""s cost, complexity and power requirements.
Thus, in accordance with U.S. patent applications Ser. Nos. 09/056,096 or 09/084,370, either narrowband or broadband services can be delivered by a small, simplified ONU. However, neither ONU is capable, on its own, of delivering both narrowband and broadband services simultaneously. Specifically, the improved narrowband ONU disclosed in U.S. patent application Ser. No. 09/056,096 does not address the traffic control problems associated with the delivery of broadband services, while the improved broadband ONU disclosed in U.S. patent application Ser. No. 09/084,370 is ill-equipped to accommodate the signal-processing demands associated with the delivery of narrowband services.
Therefore, in order to deliver a service mix containing both narrowband and broadband services, current access systems must rely on the use of two separate types of ONUs. These may be packaged in a single, larger unit or installed separately and linked in a passive optical network or ring configuration. Unfortunately for the telecommunications service provider, either option doubles the manufacturing costs associated with the access network and significantly increases the required installation effort.
As can be appreciated, there is clearly a need for a universal ONU that is capable of delivering both narrowband and broadband services.
It is an object of the present invention to mitigate or obviate one or more disadvantages of the prior art.
Therefore, the invention may be summarized according to a first broad aspect as an optical network unit (ONU) connectable between an optical fiber and a plurality of twisted pairs, the optical fiber carrying data between a host digital terminal (HDT) and the ONU, the data consisting of broadband and narrowband data destined for the twisted pairs in a downstream direction and originating from the twisted pairs in an upstream direction, the ONU comprising: interface circuitry for connection to the optical fiber, for receiving a downstream optical signal on the optical fiber and for extracting a downstream data stream therefrom; a demultiplexer connected to the interface circuitry, for receiving the downstream data stream from the interface circuitry and controllably separating it into a plurality of downstream broadband data streams destined for respective ones of the twisted pairs and a plurality of downstream narrowband data streams also destined for respective ones of the plurality of twisted pairs; and for each twisted pair: a respective broadband processing unit connected to the demultiplexing means, comprising circuitry for receiving the respective downstream broadband data stream from the demultiplexer and converting it into a respective downstream broadband analog signal destined for said twisted pair; a respective narrowband processing unit connected to the demultiplexing means, comprising circuitry for receiving the respective downstream narrowband data stream from the demultiplexer and converting it into a respective downstream narrowband analog signal destined for said twisted pair; and a respective combiner connected to the respective broadband and narrowband processing units and connectable to the twisted pair, comprising circuitry for combining the respective downstream broadband analog signal and the respective downstream narrowband analog signal into a respective downstream composite analog data signal destined for said twisted pair.
According to a second broad aspect, the invention may be summarized as an optical network unit (ONU) connectable between an optical fiber and a plurality of twisted pairs, the optical fiber carrying data between a host digital terminal (HDT) and the ONU, the data consisting of broadband and narrowband data destined for the twisted pairs in a downstream direction and originating from the twisted pairs in an upstream direction, the ONU comprising: interface circuitry for connection to the optical fiber, for receiving a downstream optical signal on the optical fiber and for extracting a downstream data stream therefrom; a demultiplexer connected to the interface circuitry, for receiving the downstream data stream from the interface circuitry and separating it into a plurality of intermediate downstream broadband data streams for connection to a downstream broadband processing pool and a plurality of downstream narrowband data streams destined for respective ones of the plurality of twisted pairs; a downstream broadband processing pool connected to the demultiplexer, comprising processing means for processing the intermediate downstream broadband data streams received from the demultiplexer and a cross-connect for selectably routing the processed intermediate downstream broadband data streams to a plurality of downstream broadband data streams destined for respective ones of the plurality of twisted pairs; and for each twisted pair: a respective broadband processing unit connected to the downstream broadband processing pool demultiplexing means, comprising circuitry for receiving the respective downstream broadband data stream from the downstream broadband processing pool and converting it into a respective downstream broadband analog signal destined for said twisted pair; a respective narrowband processing unit connected to the demultiplexing means, comprising circuitry for receiving the respective downstream narrowband data stream from the demultiplexer and converting it into a respective downstream narrowband analog signal destined for said twisted pair; and a respective combiner connected to the respective broadband and narrowband processing units and connectable to the twisted pair, comprising circuitry for combining the respective downstream broadband analog signal and the respective downstream narrowband analog signal into a respective downstream composite analog data signal destined for said twisted pair.
The invention may be summarized according to a third broad aspect as a method of transmitting data received on an optical fiber to a plurality of twisted pairs, the data arriving on the optical fiber as a series of downstream traffic elements, each downstream traffic element having a header and a body, the header indicating a destination twisted pair and a service type associated with the traffic element, the ONU comprising: determining, from the header of each traffic element, the service type associated with the traffic element; determining, from the header of each traffic element, the destination twisted pair associated with the traffic element; and processing the traffic elements and transmitting at least the body of each traffic element to the associated destination twisted pair in a data format dependent on the associated service type.
According to another broad aspect, the invention may be summarized as an optical network unit (ONU) connectable between an optical fiber and a plurality of twisted pairs, the optical fiber carrying downstream traffic elements from a host digital terminal (HDT) to the ONU, each downstream traffic element having a header and a body, the header indicating a destination twisted pair and a service type associated with the traffic element, the ONU comprising: means for determining, from the header of each traffic element, the service type associated with the traffic element; means for determining, from the header of each traffic element, the destination twisted pair associated with the traffic element; and means for processing the traffic elements and transmitting at least the body of each traffic element to the associated destination twisted pair in a data format dependent on the associated service type.
The invention may be summarized according yet another broad aspect as an access network, comprising: a host digital terminal for processing downstream data destined for an optical network unit and transmitting the downstream data thereto as a series of downstream traffic elements on an optical fiber, each downstream traffic element having a header and a body, the header indicating at least one destination twisted pair from a plurality of twisted pairs and a service type associated with the traffic element; an optical network unit (ONU) connected to the HDT by the optical fiber and connectable to the.plurality of twisted pairs, the ONU comprising: means for determining, from the header of each traffic element, the service type associated with the traffic element; means for determining, from the header of each traffic element, the at least one destination twisted pair associated with the traffic element; and means for processing the traffic elements and transmitting at least the body of each traffic element to the at least one associated destination twisted pair in a data format dependent on the associated service type.